Chemical-mechanical polishing or planarization of the surface of an object may be desirable for several reasons. For example, a flat disk or wafer of single crystal silicon is the basic substrate material in the semiconductor industry for the manufacture of integrated circuits. Semiconductor wafers are typically created by growing an elongated cylinder or boule of single crystal silicon and then slicing individual wafers from the cylinder. The slicing causes both faces of the wafer to be extremely rough. The front face of the wafer on which integrated circuitry is to be constructed must be extremely flat in order to facilitate reliable semiconductor junctions with subsequent layers of material applied to the wafer. Also, the material layers (composite thin film layers usually made of metals for conductors or oxides for insulators) applied to the wafer must also be made of a uniform thickness.
Planarization is the process of removing projections and other imperfections to create a flat planar surface and/or a uniform thickness for a deposited thin film layer on a wafer. Semiconductor wafers are planarized or polished to achieve a smooth, flat finish before performing lithographic processing steps that create integrated circuitry or interconnects on the wafer. A considerable amount of effort in the manufacturing of modern complex, high-density multilevel interconnects is devoted to the planarization of the individual layers of the interconnect structure. Non-planar surfaces result in poor optical resolution of subsequent photolithographic processing steps which in turn prohibits the printing of high-density features. If a metallization step height is too large, there is a serious danger that open circuits will be created. Since planar interconnect surface layers are required for the fabrication of modern high density integrated circuits, chemical-mechanical polishing (CMP) tools have been developed to provide controlled planarization of both structured and unstructured wafers.
In a conventional CMP tool for planarizing a wafer, the wafer is secured in a carrier connected to a shaft. The shaft is typically connected to mechanical means for transporting the wafer between a load or unload station and a position adjacent to a polishing pad mounted to a rigid or a flexible platen. Pressure is exerted on the back surface of the wafer by the carrier in order to press the wafer against the polishing pad usually in the presence of a slurry. The wafer and/or polishing pad are then moved in relation to each other by means of, for example, motors connected to the shaft and/or platen, in order to remove material in a planar manner from the front surface of the wafer.
Existing solid platens and associated slurry delivery systems (manifolds) are typically made from stainless steel (for example, 300 series stainless steel) and titanium. In the CMP process these metals are exposed to chemical environments where the pH range is from 1.0 to 14.0. Under these conditions metallic corrosion will occur. Treatments such as passivation and electropolish reduce the corrosion rate but, inevitably, all metals will corrode.
The effects of corrosion on the CMP process are unacceptable. Corrosion adds destructive particles to the slurry and could potentially damage devices on a wafer being polished. Another effect of metallic corrosion is increased defectivity beyond acceptable limits, particularly in today's environment of increasing smaller tolerances and feature size of semiconductor wafer patterning.
Consequently it would be desirable to provide a platen and slurry delivery system that eliminates metallic corrosion in the platen and manifold of a CMP system.
In addition to metallic corrosion, adhesive wear, also known as Galling, contributes to particle generation within the slurry delivery system. Galling initiates at the platen/manifold interface, and is induced by pressure and slight relative movement. As with corrosion, particle generation from Galling contributes to an increase in defectivity.
It would, therefore, be desirable to provide an improved platen/manifold interface to reduce or eliminate Galling.
It is often desirable to monitor the front surface of a wafer during the planarization process. One known method involves the use of an optical system that interrogates the front surface of the wafer in situ by positioning an optical probe under the polishing surface and transmitting and receiving an optical signal through an opening in the polishing pad. In some systems, the opening in the polishing pad is filled with an optically transparent material, or “window”, in order to prevent polishing slurry or other contaminants from being deposited into the probe and obscuring the optical path to the wafer. It is possible to adjust the planarization process based upon these real-time measurements or to terminate the process when the front surface of the wafer has reached the desired condition.
In view of the foregoing, it should be appreciated that it would be desirable to provide an improved polishing pad/platen window or lens for use in a chemical-mechanical polishing apparatus that exhibits good optical properties through which in situ monitoring of the wafer may be accomplished during the chemical-mechanical polishing process. It would further be desirable that the polishing pad/platen window or lens be easy to manufacture, easily to deploy in the polishing pad/platen, and easy to remove and replace.
Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.